Semiconductor light-emitting devices such as the light-emitting diode (LED) have continuous improvement in brightness recently, and the application is expanded from conventional signals or decorative use to light sources for various apparatus. Even in the coming future, it is possible for LEDs to replace the traditional fluorescent lamps as the new generational light source in the illuminating field.
Currently the internal quantum efficiency (IQE) of light-emitting diode is about 50% to 80%, and about 20% to 50% of the input power can not be transformed into light but become heat accumulated in the light-emitting diode. When the heat can not be dissipated from the light-emitting diode effectively, the heat results in the increase of the temperature in the light-emitting diode, and the reliability of the light-emitting diode is therefore decreased. In addition, when the light generated by the light-emitting diode can not be extracted effectively, part of the light is confined in the light-emitting diode due to the totally internal reflection and is reflected or refracted back and forth in the light-emitting diode, and is finally absorbed by the electrode or light-emitting layer which causes lower brightness.